The invention relates to an EDM method and apparatus for controlling the depth of material removal from a workpiece electrode by means of an electrode tool, wherein electrical discharge machining of the workpiece is terminated when the depth of penetration of the electrode tool within the electrode workpiece has reached a predetermined value, such that the rate of wear of the electrode tool is taken into consideration and is automatically compensated for.
It is known to manually adjust a reference position paramater, such as a depth of cut limit for example, as a function of the theoritical wear of the active face of the electrode tool. However, such a process lacks precision because it is difficult to forecast in advance what the actual wear of the electrode tool will be for each machining operation. In the course of finish machining passes with decreasing machining rates, for example, it is necessary to take into consideration a wear correction factor each time the machining rate is changed.
The present invention is addressed to a new process and apparatus which permit to eliminate the inconveniences of the prior art by providing an automatic correction of the reference position data corresponding to the actual wear of an electrode tool irrespective of the machining rate. More specifically, the present invention provides a method and apparatus for positioning the electrode tool, prior to a machining pass, in a check position wherein one of the active surfaces of the electrode tool is disposed in a predetermined reference location, measuring the parameter of that location, effecting a machining pass, following the machining pass with a new check positioning of the electrode tool under the same conditions to obtain a difference between the two locations which is due to the wear of the electrode tool, and correcting the electrode tool reference data, or depth of cut limit, in the course of the following machining passes as a function of the difference between the two check locations.